Compositions and methods of stabilizing unsaturated organic nitriles



United States Patent 3,274,231 COMPOSITIONS AND METHODS OF STABILIZING UNSATURATED ORGANIC NITRILES Tadahiro Kobayashi, Fuji-shi, Japan, assignor to Asahi Kasei Kogyo Kabushiki Kaisha, Osaka, Japan, a corporation of Japan No Drawing. Filed June 13, 1963, Ser. No. 287,516 Claims priority, application Japan, Sept. 13, 1962, 37/ 39,410; Nov. 10, 1962, 37/50,472, 37/50,473; Jan. 30, 1963, 38/3,286; Apr. 10, 1963, 38/17,627

8 Claims. (Cl. 260-4659) This invention relates to a method for inhibiting the polymerization of polymerizable unsaturated organic monomers.

It is well known that polymerizable unsaturated organic monomers are denatured when they are transferred or stored at room temperatures or subjected to elevated temperatures, such as encountered during distillation of monomers.

It is also well known that stabilizers are added to the monomers in order to avoid such denaturation. However, it has also been experienced that polymers are colored when the polymer is made from the monomers containing stabilizers, t-butylcatechol, hydroquinon and p-methoxyphenol, for example, which are familiar stabilizers for acrylonitrile, acrylates or methacrylates reduce whiteness or the thermal stability in whiteness of polymers thereof, and sometimes they inhibit polymerization to adversely effect the polymerization yield and molecular weight distribution, even if they are contained in the monomers in a minor amount. Accordingly, the monomers should be thoroughly purified before they are polymerized, with the result that they require severe distillation and consequent loss of monomer. I

It is an object of the present invention to provide new stabilizing agents for polymerizable unsaturated organic monomers which avoid denaturation of the monomers and do not color polymers obtained therefrom.

It is an other object of the persent invention to provide new stabilizing agents for polymerizable unsaturated organic monomers which give polymers superior thermal stability in whiteness, even if the stabililizers remain therein.

It is a further object of the present invention to provide a method for stabilizing polymerizable unsaturated organic monomeric compounds.

According to the present invention, compounds represented by the general formula of wherein X represents a sulphur or oxygen atom are admixed with polymerizable unsaturated, organic compounds.

The polymerizable, unsaturated organic compounds according to the invention are acrylonitrile and alkyl substituted compounds thereof, e.g., methacrylonitrile, dimethyl acrylonitrile, etc. The fol-lowing compounds are also stabilized by the substances according to the invention but are the subjects of separate divisional applications SN 482,657, 582,658 and 482,659, acrylic acid and its alkyl substituted compounds thereof, e.g., methacrylic acid, methacrylic acid, etc, and alkyl esters of such acids, e.g., methyl methacrylate, ethylmethacrylate, butylmethacrylate, methylacrylate ethyl acrylate, propyl acrylate, butyl acrylate, etc.; and amides of such acids, e.g., acrylarnide, methacrylamide, etc.; styrene and alkyl substituted compound thereof, e.g., p-methylstyrene, etc.; vinyl esters, e.g., vinyl acetate, vinyl propionate, etc.; vinyl and vinylidene halides, e.g., vinyl chloride, vinylidene chloride, etc.; vinyl compound containing sulfonic acid groups, e.g., vinyl sulfonic acid, methallyl sulfonic acid, p-styrene sul- 3,274,231 Patented Sept. 20, 1966 fonic acid, etc.; vinyl compounds containing basic nitrogen atom, e.g., 2-methyl-5-vinyl pyridine, 4-vinyl pyridine and N,N-diethylaminoethylmethacrylate.

The compounds to be added includes acetonethiosemicarbazone, acetaldehydethiosemicarbazone, acetophenonethiosemicarbazone, actylthiosemicarbazole, phenylthiosemicarbazide, formylthiosemicarbazide, carbaminylthiosemicarbazide, thiosemicarbazide, acetonesemicarbazone, acetaldehydesemicarbazone, acetophcnonesemicarbazone, acetylsemicarbazide, semicarbazide, phenylsemicarbazide and iononesemicarbazone.

The stabilizer compounds may be used in an amount of 0.5 to 2000 p.p.m., preferably 1450 p.p.m.

These stabilizers produce no adverse effects when monomers having the stabilizers are subjected to polymerization in the presence of peroxide or redox type catalysts. EXAMPLE 1 In order to show the effectiveness of the present inhibitors in comparison with other known inhibitors a test was carried out in which acrylonitrile containing the inhibitors to be compared was subjected to the oxygen bomb test, which is conventionally employed for determining the stability of gasoline in the presence of oxygen at high pressures. This test was carried out as follows:

Using a graduated cylinder, 25 ml. of acrylonitrile containing the inhibitor was introduced into the glass liner. The liner was placed in the stainless steel bomb, connected to a pressure recording guage and the bomb was closed tightly. Oxygen was added to a pressure of pounds per square inch gauge at room temperature. The bomb was placed in a steam bath and the pressure characteristics were noted over a four-hour period.

As the bomb becomes heated, the pressure rises gradually to about pounds per square inch gauge. If the sample is potentially unstable, the pressure, after level ling off, will drop, then increase rapidly, and the acrylonitrile will become a solid polymer. If no sudden pressure drop i noted, and if no solid polymer is formed during the four-hour test period, the inhibitor is considered satisfactory.

The above test was applied to acrylonitrile containing the following inhibitors. Tertiary butyl catechol, hydroquinone monomethyl ether, thiosemicarbazide, acetaldehydethiosemicarbazone, acetonethiosemicarbazone, acetophenonethiosemicarbazone, semicarbazide, acetonesemicarbazone, acetaldehydesemicarbazone. The table mentioned hereinunder shows the concentrations as well as the effect upon the acrylonitrile.

Comparison of inhibitors Tertiary butyl catechol 100 p.p.m. sample polymerized. Hydroquinone monomethylether 10 p.p.m., sample polymerized. Hydroquinone monomethyl ether 20 p.p.m., no polymer formed. Thiosemicarbazide 5 p.p.m., no polymer formed. Acetaldehydethiosemicarbazone 4 p.p.m., no polymer formed. Acetonethiosemicarbazone 4 p.p.m., no polymer formed. Acetophenonethiosemicarbazone 4 p.p.m., no polymer formed. Semicarbazide 8 p.p.m., no polymer formed. Acetonesemicarbazone 8 p.p.m., no polymer formed. Acetaldehydesemicarbazone 8 p.p.m., no polymer formed.

The above data show that the inhibitors according to the present invention are effective at lower concentrations than the conventional inhibitors of the prior art. In addition to this superiority in that a smaller amount of the inacrylate, butyl acrylate and methylmethacrylate containing the following inhibitors.

Hydroquinone monomethyl ether Thiosemicarbazide hibitors is necessary, the present inhibitorshave the fur- 5 Acetonethiosemicarbazone ther advantages of negligible color formation. In add1- Acetylthiosemicarbazide tron to the above accelerated stability test carried out in Sem1carbaz1de the presence of oxygen at elevated temperatures and hlgh A cetonesemicarbazone pressures, it has been found that the present lnhlbitors h 1 b are effective in prolonged storage under normal atmos P any Semlcar Acetaldehydethiosemicarbazone pheric conditions.

Acrylic fibre was prepared by polymerizing acryloni- The table hereinunder mentioned shows the concentratrile (containing the inhibitor), without removing the introns as well as the effect upon the acrylic esters and hibitor, dissolving in 5580% nitric acid. The thermal methacrylic esters.

Comparison of inhibitors Conccntra- Inhibited Monomers Inhibitors tions of inperiod hibitors (hour) (p.p.m.)

Methyl acrylate IIydroquinone monomethyl cther. 50 3 Do i d0 300 6 Do Thiosemicarbazide l 6 D0 Aeetonethiosemicarbazone 25 1 6 Butyl acrylate Acetylthrosemrcarbamde. o

l\letliylrnetliacrylate Thiosemicarbazide 30 n Do Semicarbazide 6 Acetonesemicarbazone- 40 1 G Phenylsernicarhazide 40 6 Acetaldehydethiosemicarbazone. 40 1 6 1 Over.

stability in whiteness of the acrylic fibres thus prepared were very good and showed negligible color formation.

EXAMPLE 2 In order to show the efifectiveness of the present inhibitors in comparison with other known inhibitor a test was carried out in which acrylic esters, such as rnethylacrylate, ethyl acrylate and butyl acrylate, and rnethacrylic esters such as methylmethacrylate containing the inhibitors to be 4 EXAMPLE 3 compared was subjected to a viscosity test which was carried out as follows: I Effectiveness of the present inhibitors were investigated.

In a 100 Eflenmfiyef flask, an lnhlbltol" and 0-025 Monomers to which the inhibitors were added weighed gram of 2,2 -azobis1sobutylon1tr1le 1s dissolved 1n 60 100 g., respectively and were left to stand under atmosgrams of acrylic ester or methacrylic ester. This flask 1s pheric pressure, at room temperature for one year, ex-

placed in a thermostat maintained at C. The viscoslty cept for vinylchloride in a bomb for one year, to observe of 5 cc. samples taken at fixed intervals from the flask is changes of viscosity as well as appearance.

Table Monomers Inhibitors Cone Viscosity Appearance Acrylonitrilc Thiosemicarbazide Unchanged-.. Unchanged. Methacrylonitrile. Acetonethiosemicarbazone do D0. Acrylic acid Acetylthiosemicarbazide. Do. Mcthacrylic acid. Semicarbazide D0. Ethacrylic acid" Acetonesemicarbazone D0. I\Iethyl1nethacrylate. Acetaldehydesemicarbazone" Do. Ethylmethacrylate Acetaldehydethiosemicarbazone Do. Butylmothacry1atc Phenylsemicarbazide Do. Methylaerylate Acetonethiosemicarbazone Do. Ethylacrylate- Thiosemicnrbazide Do. Propylacrylate. Acetonesemicarbazone- D0. Butylacrylate Acetaldehydesemicarbazone. Do. Styrene Acetonethiosemicarbazone- Do. p-Methylstyrene. Semicarbazide Do. Vinylacetate Acetaldehydethiosemicarbazone Do. Vinylchloride Acetaldehydesemicarbazone Do. Vinylidenechloride- Semicarbazide Do. Vinylsull'onic acid Phenylsemicarbazide Do. Methallylsulfonic acid. Acctonethiosemicarbazone Do. p-Styrene sulfonic acid Thiosemicarbazide Do. 2-methyl-5-vinyl pyridi -.do Do. 4-vinylpyridinc Acetaldehydethiosemicarbazonc. Do. N, N-dimethylaminoethylm Semicarbazide D0.

measured by an Ostwalt viscosimeter. When the viscosity fails to rise abruptly within 6 hours, the inhibitor is considered effective.

It will be seen from the above table that lower amount of the present inhibitors than conventional ones is sufiicient to stabilize the various polymerizable organic monomers. Furthermore, the present inhibitors do not color The above test Was applied to methyl acrylate, ethyl the monomers at 31L What I claim is:

1. A composition consisting essentially of a nitrile compound selected from the group consisting of acrylonitrile, methacrylonitrile and dimethylacryl-onitrile, and 0.5 to 2,000 p.p.m. of at least one stabilizer selected from the group consisting of acetonethiosemicarbazone, acetophenonethiosemicarbazone, acetaldehydethiosemicarbazone, acetylthiosemicarbazide, phenylthiosemicarbazide, formylthiosemicarbazide, car'baminylthiosemicarbazide, thiosemicarbazide, acetonesemicarbazone, acetaldehydesemicarbazone, acetylsemicarbazide, phenylsemicarbazide, iononesemicarbazone and semicarbazide.

2. A composition comprising acrylonitrile and 1 to 50 ppm. of acetonethiosemicarbazone.

3. A composition comprising acrylonitrile and 1 to 50 ppm. of thiosemicarbazide.

4. A composition comprising acrylonitrile and 1 to 50 p.p.m. of acetaldehydethiosernicarbazone.

5. A method of stabilizing a nitrile compound selected from the group consisting of acrylonitrile, methacrylonitrile and dimethylacrylonitrile consisting of adding to said compound 0.5 to 2,000 p.p.m. of at least one stabilizer selected from the group consisting of .acetonethiosemicarbazone, acetophenonethiosemicarbazone, acetaldehyde- References Cited by the Examiner UNITED STATES PATENTS 2,299,128 10/1942 Codd et a1 252-403 X 2,328,190 8/1943 Burk et a1 252-402 X 2,353,690 7/1944 Clarkson et a1 25242 X 2,396,156 3/ 1946 Clarkson 2529-402 XR CHARLES B. PARKER, Primary Examiner.

thiosemicarbazone, acetylthiosemicarbazide, phenylthio- 25 JOSEPH BRUST Examiner 

1. A COMPOSITIN CONSISTING ESSENTIALLY OF A NITRILE COMPOUND SELECTED FROM THE GROUP CONSISTING OF ACRYLONITRILE, METHACRYLONITRILE AND DIMETHYLACRYLONITRILE, AND 0.5 TO 2,000 P.P.M. OF AT LEAST ONE STABILIZER SELECTED FROM THE GROUP CONSISTING OF ACETONETHIOSEMICARBAZONE, ACEPTOPHENONETHIOSEMICARBAZONE, ACETALDEHYDETHIOSEMICARBAZONE, ACETYTHIOSEMICARBAZIDE, PHENYLTHIOSEMICARBAZIDE, FORMYLTHIOSEMICARBAZIDE, CARBAMINYLTHIOSEMICARBAZIDE, THIOSEMICARBAZIDE, ACETONESEMICARBAZONE, ACETALDEHYDESEMICARBAZONE, ACETYLSEMICARBAZIDE, PHENYLSEMICABAZIDE, IONONESEMICARBAZONE AND SEMICARBAZIDE. 